In general, ships such as oil tankers, cargo ships and so on carry cargos like oil to an importing country, and after the cargos are unloaded on a port of the importing country, the ship stores an amount of seawater corresponding to the cargos in a ballast tank therein. Storing the seawater in the ship is performed to adjust draft (a depth of a ship submerged into water when the ship floats on the water) and trim (front and back inclination of a ship), so as to previously prevent the balance of the ship during the voyage from being broken by the light weight of the ship after the unloading of the cargos.
In other words, if a ship does not have a predetermined weight, the draft line is lowered to the lower portion of the ship by means of buoyancy, thereby causing some problems that the propeller of the ship is exposed to fail to obtain a propelling force, a wave resistance force during the voyage is lowered to apply much load to the voyage, and the body of the ship is destroyed.
So as to prevent the above-mentioned problems and thus to obtain the balance of the ship, the ballast water is stored in the ballast tank when the cargos do not exist, and the ballast water is discharged from the ballast tank when the cargos are loaded.
Accordingly, the importing country of the cargos becomes the exporting country of the ballast water. On the other hand, the ship in which the ballast water is stored sails to the exporting country of the cargos from the importing country of the cargos and discharges the ballast water to the sea near the exporting country. That is, the exporting country of the cargos becomes the importing country of the ballast water.
By the way, the ballast water typically contains specific toxic microorganisms and bacteria existing in the sea near the exporting country of the ballast water.
When the ballast water containing the microorganisms and bacteria is discharged in the sea near the importing country, marine ecosystems may be broken, so that the international carrying of aquatic organisms by the ballast water has been issued.
Thus, the international convention for the control and management of ships' ballast water and sediments is adopted by 74 attendants in United Kingdom (London) in Feb. 13, 2004. In this convention, when the ballast water is discharged to the sea near the importing country of the ballast water, the standards for the organisms of the ballast water discharged are set. If the standards are not satisfied, the importing country of the ballast water can reject the discharging of the ballast water, that is, the reception of the ballast water. Referring in detail to the standards of the organisms of the ballast water in the convention, discharging for the aquatic organisms having a minimum size of more than 50 μm should be less than 10/1 m3, discharging for the aquatic organisms having a size in a range of 10 μm to 50 μm should be less than 10/1 ml, discharging for the toxic vibrio cholera of indicator microorganisms should be less than 1 cfu/100 ml, discharging for the Escherichia coli should be less than 250 cfu/100 ml, and discharging for the enterococci should be less than 100 cfu/100 ml (wherein ‘cfu’ is a unit forming colony).
There have been various methods for purifying the ballast water at the time of storing the ballast water into the ship and at the time of discharging it to sea, and the various methods include direct electrolysis and indirect electrolysis of seawater wherein electrolysis for the seawater is basically performed to produce disinfectants and to treat the ballast water by using the produced disinfectants.
The direct electrolysis of seawater is performed by passing a whole amount of the seawater, that is, ballast water flowing into a ballast tank through an electrobath, thereby continuously disinfecting the ballast water. The direct electrolysis of seawater is classified into direct oxygen electrolysis and direct chlorine electrolysis in accordance with the kinds of disinfectants produced.
The direct oxygen electrolysis has a disinfectant selected from the group consisting of OH*, O3 and H2O2 and has the usage electrode of BDD. The direct oxygen electrolysis has some advantages in that the installation is simple in configuration, the disinfection speed is high, the residual products after the disinfection are small, and the neutralization of the disinfectant is not needed. To the contrary, it has some disadvantages in that a high quality of filter is required, the cost of the usage electrode is high, the disinfectant do not have any residual property so that the disinfection is needed again at the time of discharging ballast water, the electrobath is easily polluted, a test for the disinfection effects is required, and hydrogen gas is explosive because of the flow of generated hydrogen into the ballast tank.
The direct chlorine electrolysis has a disinfectant selected from the group consisting of NaOCl, OCl− and HOCl and has the usage electrode of DSA. The direct chlorine electrolysis has some advantages in that the installation is simple in configuration, the residual disinfecting effects exist, and a low quality of filter is used. To the contrary, it has some disadvantages in that the control of disinfection is difficult, the disinfection speed is low, the residual products after the disinfection are made, the neutralization of the disinfectant is needed, the electrobath is easily polluted, the hydrogen gas is explosive because of the flow of generated hydrogen into the ballast tank, and the electrolysis efficiency is sensitive to a quality of water.
On the other hand, the indirect electrolysis of seawater is performed by passing a portion of the seawater, that is, ballast water flowing into the ballast tank through an electrobath to produce a disinfectant and by injecting a predetermined amount of disinfectant into the ballast water flowing into the ballast tank. The disinfectant is selected from chlorine disinfectants. In more detail, the disinfectant is selected from the group consisting of NaOCl, OCl− and HOCl, and the usage electrode of DSA is used. The indirect chlorine electrolysis has some advantages in that the control of the disinfection efficiency is easy, the durability of the installation is high, the life term of the plate is long, the residual disinfection effects exist, and the technology is very practical in use. To the contrary, it has some disadvantages in that the disinfection speed is low, the residual products after the disinfection are made, the neutralization of the disinfectant is needed, all of which are common in the direct and indirect chlorine electrolysis, and the injection of a neutralizing agent is needed together with the addition of chemicals in other chemical treatments.
The indirect chlorine electrolysis in the direct and indirect electrolysis of seawater has the properties of the residual disinfection and hydrogen stability, thereby providing higher disinfection control and installation stability when compared with the direct chlorine electrolysis, and further, since it makes use of an amount of seawater corresponding to 1/50 to 1/200 of the seawater of the direct chlorine electrolysis, the load of the electrobath and the installation area become small to allow subsidiary safety equipment to be easily installed, thereby providing most reliable and effective electrolysis results.
Hereinafter, an explanation on the apparatuses for treating ballast water according to conventional practices will be in detail given with reference to FIGS. 13 to 15.
FIG. 13 is a circuit diagram showing a schematic configuration of an apparatus for treating ballast water according to one prior art indirect electrolysis of seawater. As shown, there is provided an apparatus for treating ballast water including: a pre-processor 110 adapted to filter and separate the seawater flowing through an intake line from the sea of the outside of a ship; a pump 121 adapted to flow a portion of the seawater passed through the pre-processor 110 thereinto; a seawater supplier 123 adapted to store the seawater passed through the pump 121 and a flow rate meter 12 therein; a generator 124 adapted to perform electrolysis of the seawater supplied from the seawater supplier 123 to generate sodium hypochlorite; a storing tank 125 adapted to store the sodium hypochlorite generated from the generator 124 therein; a concentration measurer 126 adapted to measure the concentration of the sodium hypochlorite supplied from the storing tank 125; and a sodium hypochlorite supplier 128 adapted to control an amount of supply and concentration of the sodium hypochlorite supplied through the concentration measurer 126 and a flow rate meter 127 and to supply the controlled sodium hypochlorite to a ballast tank 129.
Further, the apparatus for treating ballast water includes an ultraviolet radiator 130 adapted to radiate ultraviolet rays to the ballast water at the time of discharging the ballast water stored in the ballast tank 129.
FIG. 14 is a circuit diagram showing a schematic configuration of an apparatus for treating ballast water according to another prior art indirect electrolysis of seawater. As shown, there is provided an apparatus having a ballast tank disposed between an intake line and a discharge line and a pre-processor 200 adapted to filter and separate the deleterious substances contained in the seawater flowing through the intake line, wherein the apparatus includes: a seawater converter 202 adapted to flow a portion of the seawater through an incoming pipe, to produce sodium hypochlorite therefrom, to pass the produced sodium hypochlorite through a concentration controller, and to inject the sodium hypochlorite into the ballast water through a discharge pipe; a concentration detector 201 adapted to detect the kinds and concentrations of the deleterious substances contained in the seawater passed through the pre-processor 200 and electrically connected to the concentration controller of the seawater converter 202 by means of a controller; and an injection nozzle 203 disposed in the discharge pipe of the seawater converter 202.
FIG. 15 is a circuit diagram showing a schematic configuration of an apparatus for treating ballast water according to still another prior art direct electrolysis of seawater. As shown, there is provided an apparatus for disinfecting ballast water that performs the removal or inactivation of aquatic organisms including bacteria contained in the ballast water for ships, the apparatus including: an inlet port formed at one side of the apparatus so as to flow the ballast water therethrough; an outlet port formed at the other side thereof so as to discharge the ballast water therefrom; a vortex generation baffle 320 disposed in the inlet port side; a residual chlorine concentration-measuring sensor 330 disposed in the outlet port side; an electrolysis module 310 disposed in a chamber disposed between the baffle 320 and the sensor 330 and having a plurality of electrode sets each having a pair of electrodes; a power supply part 350 disposed to the outside of the electrolysis module 310 so as to supply power to the electrolysis module 310; a pump 361 adapted to intake and discharge the ballast water thereinto and therefrom; and connection means composed of pipes and valves connected to the pump 361.
In the conventional methods for treating ballast water, however, the indirect electrolysis of seawater as shown in FIG. 13 does not have any means for precisely controlling an amount of disinfectant to be injected in accordance with a flow rate of the ballast water flowing into the ballast tank, so that the ballast water not treated, that is, the ballast water containing pollution sources may flow into the ballast tank.
Additionally, the prior art apparatus does not have any means for processing hydrogen gas generated after the electrolysis from the generator in which the electrolysis for the seawater is performed to generate the sodium hypochlorite therefrom, so that if the hydrogen gas is accumulated, it may be exploded in the ballast tank.
Further, the ballast tank is generally operated one or two times during the voyage of the ship and is stopped during most of voyage time, so that the seawater stays in the interior of the ballast tank. At this time, the generator generating the sodium hypochlorite may be polluted. However, the prior art apparatuses do not have any means for preventing the generator from being polluted, thereby causing the durability of the apparatus to be lowered.
Referring in detail to the problems appearing in FIG. 13, the prior art apparatus includes: the pump, the flow rate meter and the seawater supplier in which the pumped seawater is stored provided so as to supply a predetermined amount of seawater to the generator like a sodium hypochlorite generator adopted in a field of fresh water like water purifying plants; the storing tank adapted to store the sodium hypochlorite generated from the generator through the reaction with the predetermined flow rate of seawater supplied thereto; and the concentration measurer adapted to measure the concentration of the sodium hypochlorite stored in the storing tank and to keep a predetermined degree of concentration of the sodium hypochlorite. But the flow rate meter and the seawater supplier are not necessarily required. Unlike the fresh water, that is, the seawater generally has a constant concentration (having 1% at the boundary between the fresh water and the seawater and about 3% in general seawater), and accordingly, there is no need for the installation of the flow rate meter measuring the flow rate of the seawater and the seawater supplier storing the seawater temporarily therein.
In the same manner as in the above, there is no need for the installation of the storing tank in which the sodium hypochlorite generated is stored and the concentration measurer for measuring the concentration of the disinfectant. The reason why they are not needed is that the concentration (in a range of 500 ppm to 8000 ppm) of the sodium hypochlorite stored in the storing tank is too high to be measured by means of existing concentration measurers (which can measure 0 ppm to 10 ppm) and is decreased (the concentration thereof in seawater is decreased more speedily than that in fresh water) as time is passed. In this case, the concentration-decreased disinfectant during the idle time after the activation of the equipment is just injected without any additional treatment at the time of activating the equipment again, and even though the measurement for the concentration of the sodium hypochlorite is made by means of the concentration measurer, it is not easy to perform precise control.
Also, there is no means for recognizing a precise amount of seawater flowing at the time of flowing the seawater into the ballast tank by using the concentration controller and the pump constituting the sodium hypochlorite supplier in accordance with the measured concentration of the sodium hypochlorite through the concentration measurer, so that it is not easy to control whether how much sodium hypochlorite stored per the unit flow rate of the seawater flowing is injected. That is, a most important object of the apparatus for treating ballast water is to constantly maintain the chlorine demand (of about 5 ppm to 10 ppm) for disinfecting the ballast water in accordance with the flow rate of the ballast water flowing into the ballast tank, but the apparatus as shown in FIG. 13 does not have such means.
Further, the apparatus as shown in FIG. 13 has the ultraviolet radiator for finally reducing the ballast water discharged from the ballast tank so as to discharge the ballast water into sea, but since the linear velocity of the flow rate of the ballast water discharged from the ship is about 3 m/sec, the staying time is very short. So as to perform a reliable process, therefore, the ultraviolet radiator should have a substantially large capacity, and in order to activate the large-sized ultraviolet radiator, further, a great amount of power should be required, which is very difficult to be practically used.
Moreover, since the process as shown in FIG. 13 is carried out wherein the direct electrolysis for the ballast water flowing into the ballast tank is performed to produce the disinfectant like the sodium hypochlorite, it is very sensitive to the variations of the temperature of the ballast water, and thus, if the temperature of the ballast water is low, the electrolysis efficiency of the ballast water is drastically lowered.
The indirect electrolysis of seawater as shown in FIG. 14 does not have any means for precisely controlling an amount of disinfectant to be injected in accordance with a flow rate of the ballast water flowing into the ballast tank, so that the ballast water not treated, that is, the ballast water containing pollution sources may flow into the ballast tank.
Additionally, the prior art apparatus does not have any means for processing hydrogen gas generated after the electrolysis from the seawater converter in which the electrolysis for the seawater is performed to generate the sodium hypochlorite therefrom, so that if the hydrogen gas is accumulated, it may be exploded in the ballast tank.
Further, the ballast tank is generally operated one or two times during the voyage of the ship and is stopped during most of voyage time, so that the seawater stays in the interior of the ballast tank. At this time, the seawater converter generating the sodium hypochlorite may be polluted. However, the prior art process does not have any means for preventing the seawater converter from being polluted, thereby causing the durability of the apparatus to be lowered.
Moreover, since the process as shown in FIG. 14 is carried out wherein the direct electrolysis for the ballast water flowing into the ballast tank is performed to produce the disinfectant like the sodium hypochlorite, it is very sensitive to the variations of the temperature of the ballast water, and thus, if the temperature of the ballast water is low, the electrolysis efficiency of the ballast water is drastically lowered.
The direct electrolysis of seawater as shown in FIG. 15 does not have any means for precisely controlling an amount of disinfectant to be injected in accordance with a flow rate of the ballast water flowing into the ballast tank, so that the ballast water not treated, that is, the ballast water containing pollution sources may flow into the ballast tank.
Additionally, the prior art apparatus does not have any means for processing hydrogen gas generated after the electrolysis from the electrolysis module in which the electrolysis for the seawater is performed to generate the sodium hypochlorite therefrom, so that if the hydrogen gas is accumulated, it may be exploded in the ballast tank.
Further, since the seawater is not passed through any specific pre-processor, fouling occurs by the sludge in the seawater, thereby decreasing the electrolysis efficiency and producing the ballast water not treated.
Further, the ballast tank is generally operated one or two times during the voyage of the ship and is stopped during most of voyage time, so that the seawater stays in the interior of the ballast tank. At this time, the electrolysis module generating the sodium hypochlorite may be polluted. However, the prior art process does not have any means for preventing the electrolysis module from being polluted, thereby causing the durability of the apparatus to be lowered.
Also, generally, the electrolysis (Faraday) efficiencies are varied in accordance with the concentrations of seawater in the same conditions, and the electrolysis module normally operating in the general concentration of NaCl of 2.5% to 3% in the seawater shows a drastically decreased electrolysis efficiency at the concentration of 2.5% or less. In case of the direct disinfection wherein the electrolysis for the whole amount of ballast water is performed, accordingly, there is no means for preventing the decrease of the electrolysis efficiency, so that the treatment efficiency is determined by the concentration of the seawater, thereby disadvantageously generating the ballast water not treated.
Moreover, since the process as shown in FIG. 15 is carried out wherein the direct electrolysis for the ballast water flowing into the ballast tank is performed to produce the disinfectant like the sodium hypochlorite, it is very sensitive to the variations of the temperature of the ballast water, and thus, if the temperature of the ballast water is low, the electrolysis efficiency of the ballast water is drastically lowered.